DE2236972A1 - APPARATUS FOR COLLECTING SAMPLES OF EXHAUST GAS FROM COMBUSTION ENGINES - Google Patents

Description

In the United States of America, regulations * have been passed that stipulate that in motor vehicles to be built in 1973 and 1974 the amount of certain pollutants contained in the exhaust gases must not exceed certain prescribed values The following values are not exceeded: For hydrocarbons about 2.1 g per vehicle kilometer, for carbon monoxide about 24.2 g per vehicle kilometer and for nitrogen oxides about 1.86 g per vehicle kilometer »(* See Section 1201, Chapter XEI _t Title 45 of the Code of Federal Regulations, published in the Federal Register Volume 36, No. 128, Friday, July 2, 1971, p. ₀ 12652 ff.)

In view of these regulations, it is essential to control the exhaust gases emitted by motor vehicle engines examine and analyze to determine the amounts of contaminants it contains. They are extensive Work has been done to develop gas sampling devices and in this field of work it is known to pass exhaust gases from an internal combustion engine through a test device at a precisely controlled throughput rate, with it it is possible to determine the impurities and their

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to determine proportional quantities. As every internal combustion engine Sucks in air from the environment, and since the ambient air itself is a source of pollution, care must be taken care must be taken that the analysis accurately indicates the amount of contaminants emitted only by the engine. at In the devices for taking samples that have been used up to now, the exhaust gases are diluted with air. A proportional one Part of the diluted exhaust gas is continuously collected for analysis and for that purpose becomes a device for the removal of, which operates with a constant volume but with a variable degree of dilution Samples used. A device that meets the requirements set out by the U.S. Environmental Protection Agency is described in the aforementioned part of the Federal Register and shown schematically (see also Pig. l).

In this device there is a positive displacement pump, in particular a Roots blower present, which ensures the constant gas throughput, which is a prerequisite for proper operation of the Device is «- The volumetric flow rate is a puncture the number of revolutions of the positive displacement pump.

In devices of this type, various disadvantages and difficulties arise, which will be discussed in more detail below will. Such a device usually operates in a "hostile" environment; i.e., the exhaust gases contain both corrosive substances and particulate matter Foreign body. These materials tend to build up in the constant displacement pump, so that gradually the tight working tolerances are lost, that the delivery rate varies, and that it even leads to failure the pump can come. In view of this it is necessary., the device from time to time for the purpose of maintenance

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shutdown and cleaning. Furthermore, it is now not possible to detect leaks on the pump, the one Function of both the gas temperature and the pressure difference are to be avoided completely. This occurrence of leaks must be considered "when carrying out examinations with the help of such" known devices are, and if this source of error is to be kept within certain limits, the positive displacement pump must be in relative be re-calibrated at short intervals to, constantly to choose an accurate measurement of the gas flow rate. It was also found that the operation of such pumps In the aforementioned "hostile" environment, damage to the pumps is not only due to the presence of a corrosive effect Substances, but also due to too high 'temperatures.

In more recent times, turbine engines are becoming increasingly popular used, and of course the exhaust gases of such engines must be checked ". A device with a constant displacement "pumps of the type mentioned and described in the Federal Register would have to be extraordinary have large dimensions to the exhaust * of such engines to be able to process; here "must also be taken into account, that the pump also has to convey the dilution air to be supplied to the device.

According to the invention it has been shown that it is possible in a relatively simple manner to solve the above-mentioned difficulties; avoid and limitations when you put on · »· used the so far used displacement pump another ^device; which ensures a constant gas pressure. For this purpose, according to the invention, a venturi device is used in connection with a pump which has such a high delivery rate that there is a guarantee that the venturi device will be used in critical situations

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.Flow conditions works, d. i.e., under such conditions, that the gases in the narrowest cross-section of a Venturi tube have a flow velocity above the speed of sound reach. Anyone skilled in the art is familiar with the fact that the maximum gas flow rate that can occur in the narrowest cross-section of a flow channel, is equal to the speed of sound. From this it follows furthermore, that the grass throughput by weight reaches its maximum when the gas has the narrowest cross-section among those mentioned flows through critical flow conditions.

Since a venturi operated in this way is by nature one that works with a constant volume flow Forms device, in the device according to the invention along the Venturi tube, a pressure difference becomes effective brought sufficient to ensure that the speed of sound reached during the examination and constantly is maintained. For this purpose, a simple centrifugal fan is preferably attached to the expansion side of the Venturi tube connected, and the delivery rate of this fan is chosen so that it is sufficient to the critical To maintain the flow rate of the mixture of exhaust gases and dilution air flowing through the venturi. If necessary, it is possible according to the invention to have several parallel-connected venturi tubes Use facilities for taking gas samples; in this case, each venturi is replaced by a separate one Internal combustion engine fed, and it is preferably only a single centrifugal pump or a single centrifugal fan available.

In view of the above, the object of the invention is to provide an improved device for serving gas samples that are within a predetermined range of the flow velocity

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and the volumetric throughput are very reliable and operates in an accurately predictable manner "which largely avoids damage to critical components, and in which there is no disturbance due to the accumulation of foreign particulate matter. The device according to the invention cooperates with regard to the measurement of the gas throughput such an accuracy that the error with respect to the measured throughput is currently only $ 1, and at the same time the noise pollution is reduced and the service life of the device is extended considerably. Farther it is relatively easy to increase or decrease the throughput rate; they are already devices for a nominal throughput of about 2.830 or about 8.5 or about 9.9 m / min (normal air).

In the device according to the invention it is the opposite to the known devices not necessary to periodically carry out recalibration, and at a certain Embodiment is also the influence of temperature changes been turned off. Furthermore, different leakage losses no longer need to be taken into account. A very important one The advantage of the device according to the invention is that it can also be used without further ado for the exhaust gases to take samples from turbine trieting works.

To the basic idea of the invention and its meaning to make recognizable, it should be noted that the fluidic Properties of Veriturirohren have been known for a long time, but so far no attempt has been made to to utilize these properties to achieve the advantages mentioned above. This fact comes with a special one Significant when you consider that great efforts and high costs have been made over the past few years have been expended to provide a useful apparatus for taking exhaust gas samples, and that the stand

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of the technique mentioned above, described in the Federal Register " Device has also developed.

,1

The invention and advantageous details of the invention are shown below with reference to schematic drawings Embodiments explained in more detail. It shows:

Fig. 1 schematically shows the known device for removal shown and described in the Federal Register of exhaust gas samples

2 shows a device according to the invention in perspective for taking exhaust gas samples;

FIG. 3 schematically certain parts of the device according to FIG. 2;

4 shows, on a larger scale, in longitudinal section a Venturi tube suitable for generating critical flow conditions of the type used in the device of Figures 2 and 3;

5 schematically shows a modified embodiment in which several VenturiroJire for generating constant mass flows are connected in parallel} and

Fig. 6 schematically shows a modified one on a larger scale Embodiment in which there is no heat exchanger and which is particularly suitable for testing the exhaust gases of turbine engines.

In Fig. 1 an apparatus is shown that currently meets the requirements of the aforementioned Environmental Protection Agency and is listed in the Federal Register at the Position is described. The device according to the invention has certain components that are also used in this known device are present. As mentioned, is

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however, according to the invention, a venturi for evoking critical flow conditions exist, and this "venturi Instead of the positive displacement pump shown in Fig. 1, a centrifugal fan is assigned

In the known device according to Pig. 1, the total flow of exhaust gases, which is fed from the exhaust pipe to a connecting pipe 10 in the course of a simulated Falrrprogramm, together with dilution air fed in via an inlet 11 is metered in that the gas flow is fed to a positive displacement pump 12. Samples of G _e-mixture of exhaust and dilution air flow through conduits to containers or bags 13 and 14 · filters are there to the lines where it is needed, switched on. For example, a three-part filter assembly 15 is arranged in the air inlet 11, and filters 16 and 17 are switched on in the lines fed by probes 18 and 19 and there are three-way solenoid valves 20 and 21 which enable the gas sample flows either to the bags 14 or 13 to lead or to lead them to the outside. Furthermore, the device has leak-tight connections and shut-off devices, and there are counting devices 22 and 23 which count the revolutions of the positive displacement pump 12 during the testing process and the taking and collecting of samples.

Mixing is ensured with this approved device with a positive displacement pump with a constant delivery rate of the entire exhaust gas flow of an internal combustion engine with a certain amount of dilution air that during the entire Test process a constant volume flow through the device is directed. If a vehicle engine is working under load, a larger part of the gas mixture naturally consists of exhaust gases. The approved device is designed so that the mixture contains only a very small proportion of contaminants. With the help of the device, small samples are made

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of the gas mixture withdrawn and then fed to an analyzer, not shown. As long as the mass flow passed through the device is kept constant, a uniform amount of gas is always drawn off in this device. Since after a corresponding correction to take into account the atmospheric conditions prevailing on the day of the investigation (see the probe 18_ and the bag 14) it can be assumed that all pollutants originate from the exhaust gases of the vehicle, it enables samples to be taken from each of them constant fraction of the flue gas ■ flow to calculate the weight of the pollutants contained in the entire flue gas flow. As mentioned, when used with a constant flow rate operating displacement pump, a Roots blower, and by counting the revolutions of the pump or of the fan to obtain a first indication of the amount conveyed per unit time of the mixture. It is precisely because of the presence of this fan that the aforementioned limitations and difficulties can be attributed to which the invention is intended to avoid.

In the device of Fig. 1, the inlet temperature of the gas supplied to the combustion pump 12 be substantially constant, so that the pump as a device for Can be operated to measure a constant flow rate. According to Fig. 1, a heat exchanger H is present, which according to the Information in the drawings has facilities for both heating and cooling the gases. This heat exchanger, in which the description of further details should be superfluous, meets the requirement that the device with a constant mass flow must be fed.

During an exhaust gas test, gas samples are collected in the containers or bags 13 and 14 and analyzes are made carried out to determine the content of hydrocarbons, carbon monoxide and nitrogen oxides in the exhaust gases. To the-

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For this purpose an analyzer "is used, which is in the input is also shown schematically and "described. This analyzer is not shown here still described as it does not form an object of the invention «.

In accordance with current regulations, an emissions test is carried out assuming that from a cold start is assumed and a medium-length drive (e.g. about 12 km) in "an urban area is imitated. Here, a proportional part of the diluted delivery is made continuous for the purpose of analysis collected, and this part is diluted with air so that a constant volume is obtained.

For a more detailed description of the device according to FIG. 1 and the operating and control method to be used, refer to the said agency in the Federal Register referenced, where the device, not shown here, for performing gas analyzes is also described.

In this device, which, as mentioned, is the standard device currently in use, the difficulties and disadvantages mentioned arise, and according to the invention this is a remedy in this regard created that the air metering function of the air conveying function is separated. For this purpose, a Venturi tube for generating critical flow conditions in combination with a simple, little space is used for the metering function demanding centrifugal blower used. Such a device is described below with reference to FIGS. A device is described below with reference to FIG. 5, in which the only existing Venturi tube Device according to FIGS. 2 and 3 by several, for. B. two Venturi tubes is replaced.

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Pig. 2 shows a device by means of which very good results can be achieved. The device is housed in a housing 24 and has an inlet line 25, which is connected to the exhaust pipe, not shown, a Internal combustion engine or an internal combustion engine can be connected. Air sucked in from the environment flows from above down through a chimney 28 to a chamber 27 and from there up through a pipe 26 to with the To be combined via the inlet 25 supplied exhaust gas. The mixture of exhaust gas and air then flows through a pipe 29 to a switch 30, which is designed in a known manner as a centrifugal separator and is used to to separate fine particles from the mixture stream, which get into the device via the inlet 25 or the chimney 28. Beyond the centrifugal separator, the mixture of exhaust gas and air flows through a pipe 31 to a heat exchanger 32, from which the mixture flow through a pipe 33 to a Venturi tube designated as a whole with 34 reaches the generation of critical flow conditions. The heat exchanger is shown schematically in FIG. 1 Formed way, and it is a part of the previously known devices required to obtain gas samples in each pail is. As explained in more detail below, it is possible in a certain embodiment of the invention to use the heat exchanger to leave out. This fact becomes particularly important when samples of the exhaust gases of a turbine engine should be removed, because in this case one would need a heat exchanger with excessively large dimensions.

The device according to FIG. 2 also includes a centrifugal fan 35, which is driven by an assembly 36 with a pipe section and a clamp with the outlet or expansion part of the venturi 34 can be connected.

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The apparatus of Fig. 2 is shown schematically in Pig. 3, where the "parts concerned are denoted by the same reference numerals". The centrifugal separator 30 is in Pig. 3 not shown, but in practice it is preferred to use such a separator because it has the additional advantage of producing a uniform mixture of the exhaust gas, the air and the particulate foreign matter. According to the apparatus shown in Fig. 1 with a positive displacement pump, two probes L8A and L8B present which are arranged so as d _v ate, they carry the containers or bags, not shown, samples of the dilution air and the mixture of diluent air and exhaust gases. The fan 35 of the device according to FIG. 2 also appears in FIG. 3. The mode of operation of the device according to FIG. 3 should be understandable without further explanations. Of course, an apparatus of the type shown in Figures 2 and 3 would include filters, valves, and gas collection devices of the type shown in Figure 1, as well as the required shut-off devices. The revolution counters shown in FIG. 1 are of course not required in the device according to FIG. 3, because in this embodiment, as in other embodiments of the invention, a venturi tube is used instead of a rotating displacement pump.

In Fig. 4, the Venturi tube 3 "4 is in an enlarged Longitudinal section shown. This venturi is specially designed so that it is possible to use the correct gas flow rate to achieve, which in this case is about 8.5 m / min when the Venturi tube under critical flow conditions is operated. The shape of this venturi is the result mathematical investigations and development experiments, the further explanation of which is not necessary here as the measures in question are known and since in the present case it is only necessary to

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The gas flow rate under critical flow conditions is indicated is about 8.5 m / min.

Between its entry end 37 and its exit end 38, which is connected to an expansion section 39 and widens towards the end, the venturi has a length of about 363 mm. The narrowest cross-section of the Venturi tube s is formed by a narrow annular zone 40, the width of which, measured parallel to the axis of the venturi tube, is 2.54 mm amounts to. The inlet section, the length of which is measured from the reference line 40a to the level of the inlet opening 37 can consider, has a length of 64.21 mm. The angle at which the inlet section narrows is between the wall of the inlet section and the axis of the venturi 30 °.

The length of the expansion portion of the venturi between reference line 40b and reference line 41 in Pig. 4 is 230.13 mm, and the wall of this section is inclined from the axis of the venturi at an angle of 6 °. From the plane where the expansion section of the venturi ends, i.e. i.e., from reference line 41, expanded the Venturi tube so that its wall is inclined to its axis at an angle of 27.9 'this section ends according to FIG. 4 at the plane 38 in which the outlet opening is located.

The venturi is made of corrosion-resistant steel and has a wall thickness of 6.35 mm. That extending to .in the vicinity of the inlet 37 of the venturi Tube 33 has at its end a puddle 42, which is opposite to a similar one at the inlet of the Venturi tube trained splash 43 is arranged. According to Pig. 4th a round clamp 44 serves to pull the two paddles together and hold them in place. At the other end of the venturi is the widening outlet section on its

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Outside provided with a flange 45 with a Socket part 46 cooperates, which forms part of the housing of the centrifugal fan 35 ″. The flange 45 and the socket part 46 are made of elastic by a sleeve Enclosed material, which is held in place by a clamp assembly 36.

As mentioned, the Venturi tube 34 serves as a device for metering the gas mixture, and for the flow of the To keep the mixture constant within very narrow limits. Since the mixture of exhaust gases and. Dilution air during the entire test process flows through the Venturi tube, and since the delivery rate of the connected to the expansion section Blower is sufficient to ensure that the venturi is under during the entire duration of the test process critical flow conditions is operated, the venturi works in conjunction with the fan as one Device for regulating a constant flow rate or a constant throughput rate.

FIG. 5 shows a modified embodiment of the invention in which two arrangements of the one described with reference to FIG Kind of working in parallel, and in the case of a collecting line that is jointly assigned to these arrangements 47, "receives the gas streams emitted by two Venturi tubes 34a and 34b a single blower 35a or some other device for reducing the pressure is connected, and it is ensured that that the entire gas stream can be discharged via an outlet 43 can. Such a multiple device, which could also have more than two parallel-connected Venturi tubes, can simultaneously absorb the exhaust gases of several internal combustion engines, and for this purpose are shown in FIG. B. two connections 25a and 25b available for exhaust pipes. The probes 18c and 18d are of course connected to gas analyzers (not shown) connected.

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If gas samples of constant volume are to be obtained, this is the case with the embodiments described "so far" required the temperature of the gas streams fed to the venturi to create critical flow conditions are to be kept essentially constant. For this reason, "the embodiments according to FIGS one or more heat exchangers which are provided with devices for heating or cooling the gas streams.

Pig. 6 shows a further embodiment of the invention, which makes it possible to obtain a gas sample that corresponds to a constant percentage of the total flow rate, is shown in FIG. 6. As with the devices already described, the mixture of exhaust gases and dilution air fed to the inlet of a Venturi tube 34 ', to which a centrifugal pump 35' with an excess delivery rate connected. The gas samples are taken through a probe 19 ', which is designed as a tube 19' of small dimensions is formed and has a Venturi tube section R in the present case. There is a small one on the pipe 19 ' Fan B connected, the delivery rate of which is sufficient to meet critical flow conditions in the small Venturi tube R maintain. It can be easily shown that the gas flow rate of the small venturi R is a certain The percentage of the main flow flowing through the venturi 34 'corresponds to the flow rate of the venturi R is constant, and that it is determined by the ratio between the cross-sections of the two Venturi tubes. There the gas flow rate of each venturi is a function of the temperature of the gas mixture, and there on both venturi if the temperature is the same, no temperature compensation is required and the flow rates will be determined exclusively by the ratio between the passage cross-sections. The with the help of the venturi R and The gas samples taken by the blower B are fed to a collecting device and from there to an analyzer. One

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Device of the type described with reference to FIG. 6 proves has proven particularly advantageous in testing gas turbine engine exhaust. Therefore, the term "denotes with internal combustion engine "in the claims not only internal combustion engines, but also gas turbine engines O

Expectations;

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Claims (10)

. EXPECTATIONS Apparatus for collecting samples of the exhaust gases from engines operating with internal combustion, in order to enable the collection and analysis of the samples, with a dilution air source which can be connected to a pipe for receiving the exhaust gases of an engine and which makes it possible to produce a mixture of exhaust gases and dilution air to create, . a device for taking samples of the mixture to be analyzed and a device for regulating the flow of the mixture in such a way that the mass flow is kept essentially constant, characterized in that the regulating device is a venturi tube (34) with an inlet side ¹ and an expansion side has that the inlet side is connected to a device (29, 31 »33) for receiving the mixture, that a pump (35) is connected to the expansion side of the venturi for sucking the mixture through the venturi, and that the The pump's delivery rate is sufficient to ensure that the venturi tube causes the mixture to flow through the venturi tube under critical conditions for the entire duration of a test process * 2. Apparatus according to claim 1, characterized in that g e k e η η records that the means for obtaining samples of the mixture comprises a hollow probe (18b) with a läßinen Is cross-section, which is arranged in the mixture flow in the flow direction upstream of the venturi tube (34), and that there are containers for receiving the samples taken with the aid of the probe. 3. Apparatus according to claim 2, characterized in that a second hollow probe (löa) with a small cross-section in the flow of the dilution air is arranged so that it is possible for the purpose of analysis 309838/0805 rens to take samples of the dilution air at one point, -der in the flow direction upstream of the connection point of the pipeline (25) for supplying the A "b gases of the engine. 4. Apparatus according to claim 1, characterized in that g.e k e η η, that the pump (35) is designed as a centrifugal pump « 5. Apparatus according to claim 1, characterized in that there are devices which delimit several parallel flow paths, each of which has its own source of dilution air a separate engine can be connected that several Venturi tubes (34a, 34b) are present, each of which is the Flow paths one is assigned, and that a single pump (35a) is connected to the apparatus, which is used to to suck the mixture flowing through each flow path through the associated venturi. 6. Apparatus according to claim 5, characterized in that to the means for obtaining Samples several probes (18c, 18d) with "a small cross-section and that each of these solids is arranged to permit passage through the associated flow path to take a sample from the flowing mixture. 7. Apparatus according to claim 1, characterized geke η η ζ calibration η -e> .IbS that the device for taking samples in the region of the venturi tube (34 ¹ ) is arranged 'that a pipe (19 ¹ ) for this device one part of which is arranged to take up only a small part of the mixture, that part of the tube in the pipeline forms an auxiliary venturi tube (R), and that there is a device (B) to ensure that that Auxiliary venturi works while taking samples under critical gas flow conditions. 3 09838/0805 8. Apparatus according to claim 7, characterized in that only the ratio between the smallest passage cross-sections of the two Venturi tubes (34 · ¹ , R) determines the mass flow flowing through each Venturi tube. 9. Apparatus for collecting samples of exhaust gases from internal combustion engines for the purpose of Collecting and analyzing the samples with one that can be connected to a pipeline for receiving the exhaust gases of an engine Dilution air source for generating a mixture from Exhaust gases and dilution air, a device for extraction of samples of the mixture to be analyzed, as well as with a device that serves to the flow of the mixture eo regulate that the mass flow is kept essentially constant, characterized in that to this Device includes a venturi tube (34) which is connected to devices (29, 31t 33) for receiving the mixture, that a pump (35) is connected to the venturi tube which allows the mixture to flow through the venturi tube, and that the delivery rate of the pump is sufficient to ensure that the Venturi tube for the entire duration of a Test process is operated under critical gas flow conditions. 10. Apparatus for collecting samples of exhaust gases from internal combustion engines for the purpose of Analyzing with an inlet for supplying dilution air, one the inlet with a pipe for receiving Device connecting the exhaust gases of an engine for generating a mixture of exhaust gases and dilution air, Pipelines through which the mixture flows and in which a heat exchanger is switched on, which enables the mixture increases to a substantially constant temperature during the entire duration of a test process keep a facility connected to the piping 309838/0805 device for taking samples of the mixture after the mixture has flowed through the heat exchanger, and for collecting the samples for the purpose of analysis and with a device to regulate the flow of the mixture through the apparatus in such a way that that the mass flow is kept essentially constant, characterized in that to this Establishing a venturi (34) with an inlet side and an expansion side that the inlet side to the Pipes (29, 31, 33) for receiving the mixture is connected that'mit the expansion side of the Venturi tube a centrifugal pump (35) is connected which causes the mixture to be sucked through the venturi tube, and that the delivery rate of the centrifugal pump is sufficient to ensure that the venturi operated under critical gas flow conditions during the entire duration of a test process will* 309838/0 80 5 to Blank page